Previous controllers for balers for forming cylindrical bales of agricultural crop material have monitored the radius or diameter of the bale as it is being formed to control the bale-forming operation. An example of this is U.S. Pat. No. 5,551,218 to Henderson et al. Also, previous controllers for balers have automatically controlled the movement of a guide feed point for twine applied to the bale so as to place wraps around the bale. An example is U.S. Pat. No. 4,602,560 to Jacky, which records an operator's movement of the guide feed point during a manual or programming phase and duplicates this movement of the guide feed point when in an "automatic mode" for wrapping succeeding bales with twine. Further, a previous baler has controlled an actuator to rotate two twine guide tubes so as to apply twine from respective twine supply sources simultaneously, see U.S. Pat. No. 5,388,504 to Kluver.
In the Kluver patent, the actuator drives the two twine guide tubes in rotational movement so as to position the respective twine-outlet ends at a plurality of distinct positions A-L, as illustrated in FIGS. 3-4 thereof. The actuator is controlled using a microprocessor. The microprocessor includes, as inputs, signals from respective twine sensors, which sense each output signal upon rotation of respective sensor pulleys. The microprocessor controls the locations at which the actuator movement is temporarily halted (termed a "dwell" position) from a given period of time. Typically, the duration of the dwell is determined by counting a number of twine sensor pulses emitted on each rotation of a sensor pulley that conveys twine from a twine source to a bale, with the number of sensor pulses computed to correspond to the length of twine required to place one wrap around the circumference of the bale.
The actuator is driven at full speed between actuator dwell locations. In normal operation, an operator inputs the wrap spacings (i.e., the linear spacings along the bale of the distinct positions A-K), and the controller determines the number of sensed signals from the twine sensors that correspond to a single circumferential wrap around a completed bale. The controller then controls the movement of the actuator so as to apply a wrap at each wrap spacing by causing the duration of the dwell at each location to correspond to the computed number of signals from the twine feed sensor that correspond to one wrap. The operator may optionally designate different actuator extension positions for each dwell position (i.e., the wraps need not be equally spaced along the length of the bale), as well as any particular number of sensor pulses to be counted at each dwell position before the actuator moves the twine guide tubes to the next actuator extension position. The duration of the final actuator position will normally be longer in order to apply overlapping wraps at the positions closest to the ends of the bale in order to ensure that the twine does not become unraveled after the twine is cut and the bale is ejected from the baler.
One disadvantage of the control system in Kluver is that the motion of the actuator in placing the wraps is discontinuous. The actuator is driven at full speed between the dwell positions and is stopped at each dwell position. This inherently places unnecessary stress on the actuator and requires that the actuator motor be capable of dissipating the heat, resulting from the high currents associated with the actuator motor being repeatedly operated at nearly stall currents. This also tends to cause the spur gears, that position the twine guide tube ends symmetrically about the center of the bale, to undergo unneeded stress and vibrations resulting from the twine guide tubes being repeatedly accelerated in different rotational directions as the tubes are repeatedly started and stopped.
Another disadvantage is that the twine is inherently placed on the bale initially in a nonstable pattern when applying the "wraps," since the twine guide ends undergo a short burst of motion between each dwell position where one or more wraps are applied. This allows the twine of the "center wraps" to loosen from its initial position by slipping laterally so as to assume a more helical pattern. Another disadvantage is the requirement to measure or detect the position of the twine tubes at many discrete locations along the length of a given bale being wrapped.